How does the discovery of dark matter challenge our current understanding of physics and the laws of gravity?

 

which of the following best sums up current scientific thinking about the nature of dark energy?

(a) Most dark matter probably consists of weakly interacting particles of a type that we have not yet identified.

(b) Dark matter consists of 90% of neutrinos and 10% of WIMPs.

(c) There is no longer any doubt that dark matter is made mostly of WIMPs.

(d) Dark matter probably does not really exist, and rather indicates a fundamental problem in our understanding of gravity.

Sorry for the terrible drawing but this quistion is confusing me. I really lack the understanding of physic :(

If, in Figure 13.45 from "Physics: the Nature of Things", thesystem looked exactly the same except the surface of the oil wasmeasured to be 15 cm above thewater surface (instead of the 10 cm shown in the figure), whatwould the density of the oil be?

I need an well explained answerfor this becuase when it come to the formulas I know them all but Idont know how to apply this in such a problem

A simple pendulum oflength 2.5 m makes 5.0 completeswings in 16 s. What is